doc/src/sgml/uuid-ossp.sgml

   1 <!-- doc/src/sgml/uuid-ossp.sgml -->
   2
   3 <sect1 id="uuid-ossp" xreflabel="uuid-ossp">
   4  <title>uuid-ossp &mdash; a UUID generator</title>
   5
   6  <indexterm zone="uuid-ossp">
   7   <primary>uuid-ossp</primary>
   8  </indexterm>
   9
  10  <para>
  11   The <filename>uuid-ossp</filename> module provides functions to generate universally
  12   unique identifiers (UUIDs) using one of several standard algorithms.  There
  13   are also functions to produce certain special UUID constants.
  14   This module is only necessary for special requirements beyond what is
  15   available in core <productname>PostgreSQL</productname>.  See <xref
  16   linkend="functions-uuid"/> for built-in ways to generate UUIDs.
  17  </para>
  18
  19  <para>
  20   This module is considered <quote>trusted</quote>, that is, it can be
  21   installed by non-superusers who have <literal>CREATE</literal> privilege
  22   on the current database.
  23  </para>
  24
  25  <sect2 id="uuid-ossp-functions-sect">
  26   <title><literal>uuid-ossp</literal> Functions</title>
  27
  28   <para>
  29    <xref linkend="uuid-ossp-functions"/> shows the functions available to
  30    generate UUIDs.
  31    The relevant standards ITU-T Rec. X.667, ISO/IEC 9834-8:2005, and
  32    <ulink url="https://datatracker.ietf.org/doc/html/rfc4122">RFC 4122</ulink>
  33    specify four algorithms for generating UUIDs, identified by the
  34    version numbers 1, 3, 4, and 5.  (There is no version 2 algorithm.)
  35    Each of these algorithms could be suitable for a different set of
  36    applications.
  37   </para>
  38
  39   <table id="uuid-ossp-functions">
  40    <title>Functions for UUID Generation</title>
  41     <tgroup cols="1">
  42      <thead>
  43       <row>
  44        <entry role="func_table_entry"><para role="func_signature">
  45         Function
  46        </para>
  47        <para>
  48         Description
  49        </para></entry>
  50       </row>
  51      </thead>
  52
  53      <tbody>
  54       <row>
  55        <entry role="func_table_entry"><para role="func_signature">
  56         <indexterm><primary>uuid_generate_v1</primary></indexterm>
  57         <function>uuid_generate_v1</function> ()
  58         <returnvalue>uuid</returnvalue>
  59        </para>
  60        <para>
  61         Generates a version 1 UUID.  This involves the MAC
  62         address of the computer and a time stamp.  Note that UUIDs of this
  63         kind reveal the identity of the computer that created the identifier
  64         and the time at which it did so, which might make it unsuitable for
  65         certain security-sensitive applications.
  66        </para></entry>
  67       </row>
  68
  69       <row>
  70        <entry role="func_table_entry"><para role="func_signature">
  71         <indexterm><primary>uuid_generate_v1mc</primary></indexterm>
  72         <function>uuid_generate_v1mc</function> ()
  73         <returnvalue>uuid</returnvalue>
  74        </para>
  75        <para>
  76         Generates a version 1 UUID, but uses a random multicast
  77         MAC address instead of the real MAC address of the computer.
  78        </para></entry>
  79       </row>
  80
  81       <row>
  82        <entry role="func_table_entry"><para role="func_signature">
  83         <indexterm><primary>uuid_generate_v3</primary></indexterm>
  84         <function>uuid_generate_v3</function> ( <parameter>namespace</parameter> <type>uuid</type>, <parameter>name</parameter> <type>text</type> )
  85         <returnvalue>uuid</returnvalue>
  86        </para>
  87        <para>
  88         Generates a version 3 UUID in the given namespace using
  89         the specified input name.  The namespace should be one of the special
  90         constants produced by the <function>uuid_ns_*()</function> functions
  91         shown in <xref linkend="uuid-ossp-constants"/>.  (It could be any UUID
  92         in theory.)  The name is an identifier in the selected namespace.
  93        </para>
  94        <para>
  95         For example:
  96
  97 <programlisting>
  98 SELECT uuid_generate_v3(uuid_ns_url(), 'http://www.postgresql.org');
  99 </programlisting>
 100
 101         The name parameter will be MD5-hashed, so the cleartext cannot be
 102         derived from the generated UUID.
 103         The generation of UUIDs by this method has no random or
 104         environment-dependent element and is therefore reproducible.
 105        </para></entry>
 106       </row>
 107
 108       <row>
 109        <entry role="func_table_entry"><para role="func_signature">
 110         <function>uuid_generate_v4</function> ()
 111         <returnvalue>uuid</returnvalue>
 112        </para>
 113        <para>
 114         Generates a version 4 UUID, which is derived entirely
 115         from random numbers.
 116        </para></entry>
 117       </row>
 118
 119       <row>
 120        <entry role="func_table_entry"><para role="func_signature">
 121         <function>uuid_generate_v5</function> ( <parameter>namespace</parameter> <type>uuid</type>, <parameter>name</parameter> <type>text</type> )
 122         <returnvalue>uuid</returnvalue>
 123        </para>
 124        <para>
 125         Generates a version 5 UUID, which works like a version 3
 126         UUID except that SHA-1 is used as a hashing method.  Version 5 should
 127         be preferred over version 3 because SHA-1 is thought to be more secure
 128         than MD5.
 129        </para></entry>
 130       </row>
 131      </tbody>
 132     </tgroup>
 133   </table>
 134
 135   <table id="uuid-ossp-constants">
 136    <title>Functions Returning UUID Constants</title>
 137     <tgroup cols="1">
 138      <thead>
 139       <row>
 140        <entry role="func_table_entry"><para role="func_signature">
 141         Function
 142        </para>
 143        <para>
 144         Description
 145        </para></entry>
 146       </row>
 147      </thead>
 148
 149      <tbody>
 150       <row>
 151        <entry role="func_table_entry"><para role="func_signature">
 152         <function>uuid_nil</function> ()
 153         <returnvalue>uuid</returnvalue>
 154        </para>
 155        <para>
 156         Returns a <quote>nil</quote> UUID constant, which does not occur as a
 157         real UUID.
 158        </para></entry>
 159       </row>
 160
 161       <row>
 162        <entry role="func_table_entry"><para role="func_signature">
 163         <function>uuid_ns_dns</function> ()
 164         <returnvalue>uuid</returnvalue>
 165        </para>
 166        <para>
 167         Returns a constant designating the DNS namespace for UUIDs.
 168        </para></entry>
 169       </row>
 170
 171       <row>
 172        <entry role="func_table_entry"><para role="func_signature">
 173         <function>uuid_ns_url</function> ()
 174         <returnvalue>uuid</returnvalue>
 175        </para>
 176        <para>
 177         Returns a constant designating the URL namespace for UUIDs.
 178        </para></entry>
 179       </row>
 180
 181       <row>
 182        <entry role="func_table_entry"><para role="func_signature">
 183         <function>uuid_ns_oid</function> ()
 184         <returnvalue>uuid</returnvalue>
 185        </para>
 186        <para>
 187         Returns a constant designating the ISO object identifier (OID) namespace for
 188         UUIDs.  (This pertains to ASN.1 OIDs, which are unrelated to the OIDs
 189         used in <productname>PostgreSQL</productname>.)
 190        </para></entry>
 191       </row>
 192
 193       <row>
 194        <entry role="func_table_entry"><para role="func_signature">
 195         <function>uuid_ns_x500</function> ()
 196         <returnvalue>uuid</returnvalue>
 197        </para>
 198        <para>
 199         Returns a constant designating the X.500 distinguished name (DN)
 200         namespace for UUIDs.
 201        </para></entry>
 202       </row>
 203      </tbody>
 204     </tgroup>
 205   </table>
 206  </sect2>
 207
 208  <sect2 id="uuid-ossp-building">
 209   <title>Building <filename>uuid-ossp</filename></title>
 210
 211   <para>
 212    Historically this module depended on the OSSP UUID library, which accounts
 213    for the module's name.  While the OSSP UUID library can still be found
 214    at <ulink url="http://www.ossp.org/pkg/lib/uuid/"></ulink>, it is not well
 215    maintained, and is becoming increasingly difficult to port to newer
 216    platforms.  <filename>uuid-ossp</filename> can now be built without the OSSP
 217    library on some platforms.  On FreeBSD and some other BSD-derived
 218    platforms, suitable UUID creation functions are included in the
 219    core <filename>libc</filename> library.  On Linux, macOS, and some other
 220    platforms, suitable functions are provided in the <filename>libuuid</filename>
 221    library, which originally came from the <literal>e2fsprogs</literal> project
 222    (though on modern Linux it is considered part
 223    of <literal>util-linux-ng</literal>).  When invoking <filename>configure</filename>,
 224    specify <option>--with-uuid=bsd</option> to use the BSD functions,
 225    or <option>--with-uuid=e2fs</option> to
 226    use <literal>e2fsprogs</literal>' <filename>libuuid</filename>, or
 227    <option>--with-uuid=ossp</option> to use the OSSP UUID library.
 228    More than one of these libraries might be available on a particular
 229    machine, so <filename>configure</filename> does not automatically choose one.
 230   </para>
 231  </sect2>
 232
 233  <sect2 id="uuid-ossp-author">
 234   <title>Author</title>
 235
 236   <para>
 237    Peter Eisentraut <email>peter_e@gmx.net</email>
 238   </para>
 239
 240  </sect2>
 241
 242 </sect1>